The Peace one doesn't necessarily have to have no offensive abilities, after all, there is the mantra 'If you desire peace you must prepare for war'. Perhaps it has an attack that only does damage if it is itself hurt in that same round, like a more powerful version of Mirror Coat or something, or while it is on the field, attack damage is halved or something.

Not that it really matters, since it is never going to happen, and Nintendo will probably use their lack of creativity to come up with something really shitty as usual.